Selecting alternating records from two tables - php

Question

I have two tables in my database: events_users and events_admins. The two are nearly identical (except for a few fields). Both tables also have a promoted field (1 or 0).
+-----------------+-----------------------+-------------------+-------------------+
| events_users_id | events_users_promoted | events_users_name | events_users_date |
+-----------------+-----------------------+-------------------+-------------------+
| 1 | 0 | Users foo | 2012-11-15 |
| 2 | 1 | Users bar | 2012-11-15 |
| 3 | 0 | Users foobar | 2012-11-14 |
+-----------------+-----------------------+-------------------+-------------------+
+------------------+------------------------+--------------------+--------------------+
| events_admins_id | events_admins_promoted | events_admins_name | events_admins_date |
+------------------+------------------------+--------------------+--------------------+
| 1 | 0 | admins foo | 2012-11-14 |
| 2 | 0 | admins bar | 2012-11-15 |
| 3 | 1 | admins foobar | 2012-11-16 |
+------------------+------------------------+--------------------+--------------------+
I cannot put both types of events in one table for various reasons. However, I do want one result, as follows:
All events are ordered by date, most recent first, however an admin event comes first and always alternates with a user event (alternating every record). Promoted user AND admin events are shown first.
+------------------+-----------------------+-------------------+-------------------+
| a 3 | 1 | admins foobar | 2012-11-16 |
| u 2 | 1 | Users bar | 2012-11-15 |
| a 1 | 0 | admins foo | 2012-11-14 |
| u 3 | 0 | Users foobar | 2012-11-14 |
| a 2 | 0 | admins bar | 2012-11-15 |
| u 1 | 0 | Users foo | 2012-11-15 |
+------------------+-----------------------+-------------------+-------------------+
I was wondering if I could do this with one query, using UNION to merge the two tables (the few missing fields in the one table, I'll mark as null), however, I wouldn't know how to sort them. The only way out I see at the moment is using two different queries with a simple ORDER BY promoted DESC, date ASC, put the results in two arrays and merge them alternating with PHP.
EDIT: It seems I haven't explained my goal well enough, as the two current answers don't exactly solve my problem.
The suggested queries first give me all promoted events from one category, then all promoted events of the other type, the normal events of the one type and at last the remaining events of the other type. However, these need to alternate as well: one user promoted, one admin promoted, one user promoted, one admin promoted.... When I've run out of admin promoted events, I want one admin event, one user event, one admin event...

Answer 1

SELECT * FROM (
SELECT
'u' AS TYPE,
id ,
events_users_id AS events_users_id,
events_users_promoted AS promoted,
events_users_name AS name,
events_users_date AS date
FROM eventusers
UNION ALL
SELECT
'a' AS TYPE,
id,
events_admin_id AS events_admins_id,
events_admin_promoted AS promoted,
events_admin_name AS name,
events_admin_date AS date
FROM eventadmins
) AS tmp
ORDER BY ID, TYPE DESC
Check out this http://www.sqlfiddle.com/#!2/5b9a5/10
One more column added to both the tables.
CREATE TABLE `eventusers` (
`id` INT(10) NOT NULL AUTO_INCREMENT,
`events_users_id` INT(10),
`events_users_promoted` INT(10),
`events_users_name` varchar(50),
`events_users_date` date,
PRIMARY KEY (`id`)
);
CREATE TABLE `eventadmins` (
`id` INT(10) NOT NULL AUTO_INCREMENT,
`events_admin_id` INT(10),
`events_admin_promoted` INT(10),
`events_admin_name` varchar(50),
`events_admin_date` date,
PRIMARY KEY (`id`)
);